Radio receiving system



Marsh 12, 1929. L. LEVY 1,705,412

RADIO RECEIVING SYSTEM Filed Nov. 9, 1925 2 Sheets-Sheet l March 12, 1929. L. L V 1,705,412

RADIO RECEIVING SYSTEM Filed Nov. 9, 1925 2 Sheets-Sheet 2 Patented Mar. 12, 1929.

UNITED STATES PATENT-"OFFICE.

LUCIEN LEVY, OF PARIS, FRANCE.

RADIO InEenrvnve SYSTEM.

Application fi ledl q'ov ember 9, 1925, Serial No. 67,961, and in France November 15, 19M.

,The receiving stations for electric" trans missions at high frequency suchas are used for instance inwireless telegraphy and telephony comprise anumber of oscillating c rcuits, Working at least on two frequencies one of which is the high frequency of the transmitted waves and the other an audio frequency allowing the signals to be heard.

I have previously described, for nstance in my British Patent No. 143,583 wlreless receivers, usinginot, only the two above mentioned frequencies but also intermediary frequencies between the said,frequencles whereby the current produced in the receiv ng c1rcuit can be modulated either in amplitude or in frequency; this modulation at an intermediary frequency can be either impressed on the incoming waves themselves or be,pro

duced by beats with local auxiliarycircuits. The latter arrangement using an interme: diary frequency can constitute the superheterodyne method a I The use of such intermediary frequencies provides, as shown by me and as confirmed by practice, the elimination of all strays .due chiefly-to atmospheric disturbances I h The object of my invention is an improved method for eliminating the natural oscillations arising in receivers under the action of strays, even if small aerials are used.

Another obj ect'of my invention consists in novel means for. producing the intermediary frequency. 4 f I Up till now the elimination of strays has been hindered by the following drawbacks- The aerials receiving the waves must be large in order to absorb sufiicientenergy for actuating the receiver. Such large aerials also absorb considerable energy due to strays.

Now, the aerials are generally tuned to the frequency of the incoming waves or at the most are detuned with reference to-it by a constant amount after a first tu ning to it.

. This does not allow an easy selection of the two waves received under the same conditions by the antenna and produced one by the transmitting station and the other by the strays. 1 According to my inventionI create adifference between the natural oscillations caused by theistrays due to atmospheric dis turbances for instance, and these forced by the waves transmitted by the transmitting station. This difference is based on the fact that the natural'oscillations have always the same frequency as the receivingcircuit where-- as the'forcedoscillations have that of the transmitting station. new method con sists thereforein constantly varying, periodically or not, by means disclosed hereinafter, the natural period. 7 of the circuit. Thus the natural oscillations produced by atmospheric disturbances forinstance will'have a periodi -1 cally varymg frequency 7". On the contrary the forced oscillations due to the transmitted waves willha-ve a constant frequency f; the variation of the. natural period of the receiving circuit will onlyhave for effecta periodic detuningthe only result ofwhich will be a periodic weakening to a small extent ofthe amplitude of theseforced oscillations.

. Thus a considerable difference will be-cre ated between thetwo kinds of oscillations; those due to strays will have a periodically changing frequency, that'is they are modulated in frequency whereas those due to they transmitted waves. keep a constant frequency with a periodically varying amplitude. i; e'.- they are modulated in amplitude.;' It should benjoted that these two above described modu lations have the same frequency which is that of the variations of the-tuning of the receivingcircuit,,This1frequency F will beterm'ed hereinafter the secondary frequency.

It iseasy to separate the two oscillations. After detection the modulation in amplitude can easily appear in a circuit .tuned'to the secondary frequency F of this modulation whereas thestrays will onlyproduce in such v acircuit very low frequency beats, as explained hereinbelow. The modulation in am-.

plitude will, asalso. explained hereinbelow,

be produced at a frequency F or QF'andca-n 1 be either audible or not and in the latter case as high as may be desired.

The natural period of the receiving circuit can be modified at a secondaryfrequency F either by mechanical or electrical means. (Me- 1 chanical means can only be used for lowfrequencies and can be adapted to vary, by suitable short circuits for instance, the-self induction or capacity" of the circuit; For 7 higher secondary frequencies, 1t ls'necessary through it (vacuum tubes for instance).

(1)) Variation by electric means of the value of induction coilsor condensers con effects of strays before and after detection.

Fi 7 shows the known arrangement of an electromagnetic telephone used as a detector. I

on Fig.' 1 are shown diagrammatically a first vacuum tube 1 with its filament 2, its

' grid 3 and its plate 4, a second'tube 5 with its filament 6, its grid 7 and its plate 8.

s The filaments of thetwo lamps are heated by the battery 9 and the plates are connected I through the battery 10 with their filament.

The receiving circuit comprises in series an aerial A, a coil 11, a condenser 12 and two induction coils 15 and 16. The receiving circuit is connected through the condenser 13 to the grid 3 of the lamp 1. This grid is itself connected thnough the resistance 14 toone end of the filament, whereby the tube 1 is mounted in the known'manner as a detecting tube.

The two induction coils 15' and 16 are wound in opposite directions around an iron core 18 forming a'closed magnetic circuit. A tllllCl' winding 171s also wound around this core and 1ts ends are connected to a I battery 26 and to local oscillations generator 19 working at the secondary frequency F. This frequency is much lower than that of the transmitted waves. iIt may be for in- I stance of-10,000 periods per second.

This generator 19 diagrammaticallyshown on Fig. 1 can be a mechanical device for sufficiently lowv frequencies; For higher frequenciesone' or more vacuum tubes should be used as generators.

In the plate circuit of the tube 1 are inserted the feed-back coil 20 inductively coupled with the coil 11 and the oscillating circuit21, 22 tuned to a frequency 213, double of-that of the generator 19.

The oscillations of this circuit 21, 22 are detected by the vacuum tube 5 connected as a detector and provided with the grid condenser'23 and resistance 24. i

I In the plate circuit'of the tube 5 is disposed the telephonic receiver 25.

' The direct current fed by the battery 26 in the winding 17 produces in the core'18 a magnetic flux the value of which can be adjusted so that the increases or-decreases of the flux under the action. of the alternating current of frequency F produced by the generator 19' producein the'core 1 8 variations of its permeability; to the variations of the permeability correspond variations of the self induction "of the coils 15 and 16 and thereby of the frequency f of the natural oscillations of the receiving circuit.

The device can be arranged in a manner such as will'preven't the alternating'current produced by 19 from having any effect on the coils 15 and 16 beyond this variation of permeability. This current producesinthe core 18 aperiodicunagnetic flux having. a givenwavelength. It issuflicient to disposethe coils 1'5 and 16 over the core 18 at a distance equal to thisimagnetic wave length for the fluxespassing through each of them to be in phase. Thereby and by reasonof their opposite winding, the currents induced by them will always be opposedto each other and theirresultant will be constantly zero.

On the. other hand, due to the high frequency of the waves received'by the receiving circuit, each coil15 and 16 will induce in the core 18 a magnetic flux of verysmall wave length. The two fluxes 'being'opposed will have a resultant equal to zero.

It is easy, by referring to Figs.*3 .and 4, to understand how the incoming waves will be modulated in amplitude, on these figures, the'abscissae along OX give'the times, theordinates above the line OX the variable natural frequencies f of the receiving circuit andthe ordinatesbelow OX the amplitudes of the received waves.- y

The variations of f are shown by the curve I, a sinusoid for instance,-an d its period is that of the variations of frequency, that is is more in tune. This amplitude will thus pass.

of the curve 7; or otherwise stated, in the present case, the frequency of the modulation in amplitude will be double the secondary frequency F. j I

On the contrary if-the tuning is such as will make 7 equalor superiorto the maximum (at) through a minimum, each time 7" of f or else equal 01 inferior tothe minimum of f as shown on Fig. 4, the naxiina and ininim'a'of the amplitudes will correspondto thoseof the frequencies f and'thereby in this second case the frequency of the moduli.- tion in amplitude will be "equal tothe sec o'ndaryfrequency F. f

These properties do not presuppose that the curve'givingf is a sinusoid. It is su'fli- 'CIQIlt; for this curve to be periodlcal, its freqr'iencybeing F.

The tuning variations corresponding to the amplitude of the curve f can either go up to several thousand periods per second or go down below one period in which latter case itis a mere phase variation. If it-is feared that the reception may be disturbed by stations working-at a "frequency near f, it is necessary to choose a very small amplitude for this tuning variation so as to be" always 'sufliciently detuned with reference to the disquency and slowly damped as shown on Fig. I

5.; After detection by the tube 1 each damped wave train will diminishthe mean plate current. This current passingthrough the circuit 2l22 cantherefore be represented by the curve shown onFig. 6. This curve is periodical and its frequency is very small; It is equal to the frequency-of theseveraljwave trains caused by the atmospheric disturbances; that is from about 15 to 20 per second;

This succession of shocks due to strays will have but little effect on the circuit 2122 as explained hereinabove and experimentally proved by myself with superheterodyneapparatus; these allow like that shown on Fig.

1 but by different meanst the modulation at a secondary frequency of the'oscillations of the receiving circuit.

If the incoming waves are produced by a radiotelephonic station, the modulation at an audio frequency of the waves sentout' by the transmitting station is transmitted to the currents of secondary frequency F or 2F passing through the circuit 21-22; after detection by the tube 5, the telephone reproduces these modulations at audio frequency.

In the case of radiotelegraphy, if the incoming waves are undamped and non-modulated, the coupling between the coils lljand 20 allows the tube 1 to work as a generator and a slight detuning' with reference to its tuning frequency of the circuit 11, 12, '15, 16 v allows the'production-of beats at audio 'frequency by the autodyne method between the incoming waves and the local wavesfof val-i able frequency inthe circuit 2l22, v

Fig.2 shows anothermodification of the invention wherein thevariation of the natural frequency of the receiving circuit is produced by means of vacuum tube 26 which actssimultaneously as a generator of current at]superaudible frequency and as'a'modulator; This Vacuumtube 26 is provided with a filament 27, a grid 28 and a plate '29; it is, mounted'as-a" generator by means of the induc'tion coils 3031 and the con-denser 32, the

frequency ofth e oscillations produced being superaudible; a*variable condenser 33 conneets 'the'plate of the tube 26 with the extremity of the coil 15 of the circui.t 11, 12 15 similar to that of the Figure 1'-'an'd-in which is inserted an aerial A.

- The plate-filament circuit of the tube 26 shunts the coil 15 and th'e'varying resistance of this circuit produces variations in the naturalfrequency of the circuit 11, 12 15, containii'ig the aerial A. The workingwill thus bethesame as in the case of- Fig. 1. v

' On Fig. 2 is shown between A Band A B an artificial'line" constituted by a'series of oscillating circuits and'ada'pted to damp out the low frequency shocks. The detecting tube5 is not shown asit is mounted exactly as shown in' Fig. 1. i

It can be seen thatthe circuit 2l22 of theFig. 1 is traversed by currents the frequency of which is intermediate between that of the incoming. waves and the audio-fre-v quency received in the telephone as is the case in the intermediate frequency circuit of the superhete'rodyne arrangement; it is therefore easy to understand that the improvements already proposed-for the superhetcrodyne receiver can be applied to the receiver disclosed in this specification. For instance selective or non-selective-amplifiers can bedisposed.

for each frequency; the number of frequenones being above two, the final amplification Wlll be far higher than that-provided by an ordinary apparatus using only the high frequency of'the transmitted waves and the audio-frequency allowing the signals to be heard. 1 The circuit 2l22 can be replaced by an artificial line or'by any other combination of oscillating circuits. i The known heterodyne, superheterodyne and superregenerating methods canbe, if desired, used with the abovedescribed receiver. For; instance, the primary circuit 11, 12,".155 16 can be submitted to the heterodyne method through the coil '34 (Fig. 1) coupled thereto and thefsccondary circuit 2l22 through'the coil 35 coupled thereto.

It should be noted that the dificrent steps with constituting the method applied to my receiver can be repeated several times in the receiver. My improved receiver can be considered as a frequency changer and it is evident that-between the original frequency f and the audio-frequency actuating the tele some by the above described methodand some by the superheterodyne'method.

In the case of short'waves the autodyne method can be used insteadof the heterodyne method. 7

In thecase of short waves, as is'well known, very small changes in the frequency at the transmitting station can make the signals vanish at the receiving station. This is the case for instance for the receivingdevices comprising circuit-s having a very'great feedback such as the superregenerating arrangements. In those cases the above described method is of great interest as the natural frequency of the receiving circuit varies slightly on either side of a mean value. This provides for a sort of periodical exploration of a field, of frequencies on either side of fm and the correct tuning is passed through twice per period whereby the signals are received with certainty near these passages through the correct tuning frequency.

It should also be noted that the method can be applied in all cases where a circuit can be traversed by natural oscillations in view of preventing these oscillations to act on the following circuits. For instance, it can be applied to all oscillating circuits, artificial electric or magnetic lines, transmission wires using carrier waves etc.

Evidently, the variation of the natural frequency of the receiving circuit can follow any law'and the curves I of Figs.-3-and 4 can be replaced by any desired curves. For instance the natural frequency ofthe receiving circuit (or circuits) can be changed suddenly; this. can be done for instance by disposing a valve'in the circuit of the generator 19 and of the winding 17. v

An interesting improvement in the described method consists in replacing the secondary detector (tube 5 of Fig; '1) by an electromagnetic telephone which acts in the same manner. This telephone (Fig. 7) comprises two windings; the stationary one 36 serves to vary the magnetic field wherein the coil 37 to which the vibratingdiaphragm 38 is secured is adapted to move. Current is fed from the generator 19, for instance, into the stationary winding 36 and from the plate circuit of the tube 1 into the movable coil 37. The receiving circuit should be adjusted so, as to make the frequency of the nodu-g lation in amplitude equal to the secondary frequency F and not toa multiple thereof. j

tions (phase variations for instance) thecurrent of secondary frequencymay act on the local current of the modulator or'ofthe heterodyne generator in a radio goniometer l/Vhat Iclaim is:

1. A stray proof radio receiver comprising a receiving circuit, means for varying automatically in acontinuous manner according to apredetermined periodicallaw. the'natural period :of said receiving circuit with reference to the periodof the incoming waves, means adapted to substantially quench :the natural oscillations at varying frequency transmitted .by the receiving circuit and to allow the forced oscillations thereof .at the frequency of the incoming waves to pass and means for detecting said forced oscillations.

2. A stray-proof radio receiver comprising-a receiving circuit, means for varying-automatically in a continuous manner according to a predetermined periodical ,law the natural period of said receiving circuit with reference to the periodoftheincoming waves, detecting means adapted to receive the current from the receiving circuit, anoscillating circuit fed by the detecting means and tuned to a frequency which is in a simple ratio with that of thevariations of the natural period of thereceiving circuit, second detecting means fed by the oscillating circuit and a receiver proper fed by said second detecting means.

3. A stray ,proof radio receiver comprising a receiving circuit, a generatorof oscillations insertedin shunt with part of the receiving circuit and causing the natural period thereof tovary automatically in a continuous manner according to a predetermined periodical law with reference to the period of the incoming waves,.means.adapted to substantially quench the natural oscillationsat varying frequency transmitted by the receiving circuit and to allow the forced oscillations thereof at the frequency of the incoming waves to pass and means for detecting said forced-oscillm tions.

4. A. stray proof radio receiver comprising a receiving circuit, means for varying auto matically in a continuous manner according to a predetermined periodical law the natural period of said receiving circuit with reference to the period of the incoming waves, the superaudible period of the variation of the natural period being much lower than that of the incoming waves, means adapted to substantially quench the natural oscillations at varying frequency transmitted by the receiving circuit and to allow the forced oscillations thereof at the frequency of the incoming waves to pass and means for detecting said forced oscillations,

- i 5. A stray proof radio receiver as claimed in claim 1 comprising a number of circuits at intermediary frequencies between that of the incoming waves and audio frequency, means v20 for producing some of these intermediary frequencies by a continuous periodical variation of the higher frequency, detecting means applied to said higher frequency, and means for producing the remaining intermediary frequencies through a frequency changer.

6. A stray-proof radio receivercomprising a receiving c1rcu1t', means for varying automatically in a continuous manner according I to a predetermined periodical law the natural of the natural period of the receiving circuit,

second detecting means fed by the oscillating circuit and a receiver proper constituted by an electromagnetic telephone one Winding of which is'fed by the said'oscillating circuit and the other by a current having the same period as the variations of frequency in the receiving circuit. v

In testimony whereof I have signed my name to'this specification.

' LUCIEN LEVY. 

